Brush-holder.



I BEST AVNLABLE @om No.7|4-,an. Patented Dec. 2., |902. 1 f i w.v n.x.lTcHFlsLn.

Axsausa Howes.

, (Applicntixm ed Apr. 30, 1901.)

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eEsT Amr/ABLE- com .,U-NrrE-nl STATES PATENT OFFICE.

WALTER D. LITCHFIELD, or scnizsno'rnnr, New 1'onn, Ass1cNOR 'ToGENERAL'ELECTRIC COMPANY, A CORPORATION or New YORK.

"BRUSH-HOLDER.

, fsPCIYFiccrIoN forming vpm ef Letters patent No. 714,811, ateaDecember 2, 190e.

Be it known that I,WALTERD. LITCH FIELD, a citizen of the United States,residing at.

" Schenectady, county of Schenectady, State of New York, have inve'n-*edcertain new and useful Improvements in Brush-Holders, (Case No. 2,159,)of which the following a specifica- This invention relatestoimprovements in brush-holders for.electric machines; and it .g consistsina novel means for preventing the overheating and consequent decreaseof resiliency of the Springsgvhich are combined with the brush-holdersto 'force'pthe' brush against the commutator or collector ring of themachine.

It .is well known thatthe temper or re siliency of metal is impaired ortotally deetroyed by'heatinv. It is essential that a spring be employedin brush-holders for the purpose ofmaintaining the brush in goodelectrical contact with the commutator or col- A lector, andthesesprings are almost always in electrical connection with thebruslnand consequently take current. A good spring hasconsiderableresistance, and consequentlybecomes very hot, so that itsresiliency is impaired. One of the most serious problems with whichconstructors of electrical inachines have had to deal is that ofpreventing this decrease of resiliency. In some classes of work anadequate remedy has been provided in the form of flexible braided-wirevleads or cables, which are secured to the carbon brushes generallyemployed and to some condu'cting portion of the brush holder.

' These iiexiblc leadsvare familiar-ly known in the art as pigtails'.AIn certain other classes of worl, however-such as railway-motors,

in connection withwhich this invention was lmadethe brushes becoxnesohotthat the cou- Y sppiicatiantieuprn30,1901. anni 110.521.153. hameauvention which is incompatible .with its use in connection with auauxiliary cable, and, in fact, the drawings herein disclose anapplication of the invention in combination with a cable of the typewhich is securedto an auxiliary contact-piece which bears on the vtopofthe brush. .In such cases the invention serves as an additional meansfor the `preservation of the life of the spring; but iu' cases where theflexible cable is not employed at all the invention maybe so utilized asto shunt practically all the current from the spring.

The invention comprises a piece of good conducting metal, such ascopper, which is combined with a brush-holder spring in such manner thatthe current which would otherwise flow through the spring to heat it anddestroy its spring 'qualities will be shunted through the piece ofcopper.

The'leads or cables which have hitherto been employed for the purpose ofshunting current from the springs have, as described above, been madeflexible in order to permit free movement of the spring, so that' thelatter could follow the downward movement of the brush toward thecommutator when the brush wore away. rllhe same movement of the springshould be permitted in all cases, and hence the piece which is combinedwith the spring iu accordance with this invention should be of ductilemetal, and for this purpose I prefer to employ copper, which is atv oncethe most ductile and highly conductive. of metals. A

inasmuch as the object of the invention is to prevent the brush-l1olderspring from be-A coming veryhot, it is desirable that the auxiliarymetal piece should be a good conductor of heat in order to abstract theheat from the spring. Again, l prefer copper for this purpose, becausein addition to its properties oi' d uctilit-y and electric conductivityit is also a very good conductor of heat..

'lhe drawings herein disclose a spring' which comprises a flat stripwound into a spiralicoil, which is th'c best embodiment of my inventionknown to. me, but the invention in its broader aspect may be employed inpractice in combination with any other form of spring, as the stri pneed not be coiled,

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but may be a'ilat spring, and the Aspring itself might be of any' othercross-'sectional out- 1iue,or resili'entmaterial of any desirableoutlinewhatsoever might be coiled helically' instead 'of spirally-.1

Of the drawings, litigare)A ispan' elevation of a,hrush-holder embodyiu"the invention,

and Eig.: 2 is a perspective view of the spring" shown in Fig. 1 andconstructed in one of.

lo the numerous ways .which the invention will frame of the machine bymeans of the partssuggest to thos'e skilled iny the art.

Thelbrush-holder H is suitably mounted 'on and insulated from theportion X of the x5 D, E, F, and G and has an insulatorl interposedbetween itself and said parts in accordance with the'commonly-employedmethod disclosed vin the patent to Priest, No. 648,052.

, The brush B is free to move up and down 2o through the brush-holderand is adapted to 'engage thesegmeuts of the commutator M.`Currentistaken from the brush-holder by the lead Y, secured by the boltZ. The coustruction described up to this point is already well known' inthe art.

. The spring S is arranged to force the brush 'through the holder`against the comm ut-ator l and is iu electrical connection with the'brush, \s'o that `it takes current'. In the example 3o shown the springis a flat strip, a'portiou of which is coiled into a spiral, the end Uof the sp ring in the center of the coil being straight and adapted tobe secured in a slot in the stud 4o conductor.

I material.

that my invention .may be most usefully em# ployed in connection with aspring of this A fiat strip A, preferably of copper,is placed upon thephosphor-bronze spring,

so that it lies in contact therewit.li,'aml in the particular typedisclosed herein the copper strip is wound -with the spring and rivetedv thereto. I n testing the invention I employed 5o asprug of Scovillebronze iive-eighths of au inch wideand one-sixteentlrof an inch thick.

The popper strip was also 'live-eighths of Van inch wide and vthreeone-hundredths of an inch thick, and when wound in parallel with thebronze spring the copper strip had five times the conductivity of thespring, and hence it is obvious that most of the current was shuntedfrom theI spring, with the result that it did not become oven-heated.The cop- 6o per strip being such a good comluetor may be sovery thinthat it will interfere in no way with the free movement of the spring S,especially alsoas copper is most ductile, so that the spring cau movefreely to keep the brush in engagement with thc segments ol' the commutator.

As shown in thc drawings," the copper strip extends on both sides of thespring for a considerable portion of the length of the latter, and asthe copper strip is a goed conductor .of heat and has alarge extent ofsurface cx- 4posed tothe air it is evident that in this arrangement thelittle heat rhich may be developed in .the spring by the passagetherethrough of a small current will be absorbed by the copper strip anddissipated therefrom by radiation and convection. A'The spring thus maybe used in cases Where a'pigtail is secured to the brush-holder for thepurpose of coperatingwith the pigtailinshuntingcurrentfrom the springand to serve as a safeguard in case the brush should become so hot thatthe connection of the pigtail with it might be destroyed. The inventionmay also be used, as shown in the drawings, in cases where it is notdesired to have the free end of the spring engage directly with the topof the brush in order to prevent the poor contact which sometimesresults between the spring and the brush. In such cases a separatecontact-piece C bears o`n the top of the brush and the spring presses onthis contactpiece. Thus a uniformly good contact is provided between thetop of the brush and the contact-piece; but in order to provide a betterpath for the current than that betu'eenthe contact-pieceand the spring aflexible lead P, consisting of a braided-Wire cable is secured to theportion J of the coutact-piece C, as shown in Fig. '2. Since the springis, in accordance withthis invention, provided with the copper strip A,the cable P may be attached to the' strip A by means of the clip L andthe rivets R. The reinforced spring is lient atits free end, and thebent portion is adapted to rest ou the contact-piece C and to be heldthereto by means 4ot a pin N, which passes through the holes O and theportion J of the contact-piece C. Thus two paths for the current areprovided from the contact-piece C, but they join at the copper strip A,so that all the current flows through the reinforced spring, which itmay safely do owing to the copper strip.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is-

l. The combination with a brushlholder, of a contact-piece arranged tobear on the top of the brush, a spring arranged to bear on thecontact-piece to force the brush against the commutator, a piece of goodconducting metal provided with an auxiliary conductingstrip IOO'arranged in contact with the spring to shunt current therefrom, and ailexible connection between the contact-piece and said piece ofconducting metal. l

2. The combination with a brush-holder, of a slotted stud, and a springcoiled about said stud having one end bent to engage in said slot-andthe other cud adapted to force the brush against the comniutator, saidspring Acomprising.; a flat strip of resilient metal, and

a strip ol'good conduct-ing xnetai arranged in contact with theresilient strip to shunt lurrcut therefrom.

714,8@EST VALABLE CPX 4.. The combination with a brush-holder, of

xo a contactfpiece arranged to bear against the bmah, a springarrangedlobear onthe contact-piece, a piece of good conducting metal toshunt current around the spring, and a fiexible connection between thecontact-piece and said piece of conducting metal.

In Witness whereof I have hereunto set my hand this 29th day of April,1901.

WALTER D. LITCHFIELD.

Witnesses:

BENJAMIN B. HULL, MARGARET E. WooLLEY.'

